This application investigates pathologic mechanisms in retinopathy due to diabetes mellitus. A hallmark of diabetic retinopathy is extracellular matrix (ECM) accumulation, basement membrane thickening, and increased turnover of the normally quiescent endothelial cell. Previous studies from the applicant's laboratory support the hypothesis that a contribution to basement membrane thickening is made by over-expression of proteinases. Retinal endothelial cells exposed to diabetic conditions including aberrant ECM demonstrate increased cell death and new cell proliferation. Mechanisms responsible for the co-existence, within very close proximity, of acellular capillaries in non-proliferative retinopathy and neovascularization in proliferative disease are not understood. However, interactions between the secreted ECM, integrins, and cell surface growth factor receptors are likely to determine cell survival. Studies with a unique human retinal endothelial cell (HREC) culture system permit comparison of cell responses between tissues from diabetic and non-diabetic donors and lead to the following hypothesis: the excessive ECM associated with diabetes mellitus promotes aberrant integrin and growth factor receptor expression in retinal endothelial cells, which can stimulate proliferation or apoptosis. Four approaches are proposed to test this hypothesis: (1) characterization of ECM components produced by cultured cells from normal and diabetic donors and testing the hypothesis that the diabetic ECM affects growth factor expression; (2) characterization of the effects of different ECMs on integrin expression and evaluation of which integrins permit growth and which contribute to apoptosis; (3) determining the effects of the survival factors, IGF-1 and VEGF, on prevention of HREC apoptosis; and (4) examining the effects of selective growth factor receptor and integrin ablation by hammerhead ribozymes on cell signaling. It is hoped that results will generate new information on the regulation of retinal endothelium in diabetes that may lead to more rational therapeutic intervention.